A TOF camera system should not only comprise systems, which directly determine distances from the time of flight but in particular also all TOF or 3D-TOF camera systems which obtain runtime information from the phase shift of an emitted and received radiation. PMD cameras with photonic mixer detectors (PMD), as they are described in the applications EP 1 777 747, U.S. Pat. No. 6,587,186 and DE 197 04 496, among others, are in particular suitable as time of flight or 3D-TOF cameras and are available, for example, from, “ifm electronic gmbh” as Frame-Grabber O3D. The PMD camera in particular permits a flexible arrangement of the light source and of the detector, which can be arranged both in a housing and also separately. Naturally, cameras or devices with at least one reception pixel, like for example the applicant's distance measuring device O1D should also be comprised in the concept of camera and camera system
In a TOF camera system in which the illumination and the camera are arranged in separate modules, it is necessary to connect both modules to each other also with respect to a data exchange. In the simplest case, at least the common modulation frequency is to be exchanged via a data line between both modules. In particular, for safety concerns it is of special interest to also exchange safety-related data between the modules, so that, as a rule, several forward and reverse channels must be built between the modules. The data channels can, for example, be constructed as a CAN bus or also as a low voltage differential signal line (LVDS).
The transmission of data via an LVDS line is of special interest, since this transmission is robust against external interferences because of the differential signals. Here, the transmission must not strictly occur at low voltages, namely <5 volts, but it can also be performed at higher voltages. In the case of an LVDS signal transmission, the signal is transmitted via the voltage difference between two signal lines. Since for signal evaluation purposes, only the difference of the voltages on both signal lines is evaluated, the interferences acting equally on both lines have practically no influence on the data signal. Because of the very good interference signal suppression, the differential signal can be reduced, if necessary, to less than 100 mV. This permits, for example, a faster data rate because of the faster rise time.
The use of an LVDS transmission line for a PMD camera system is known, for example, from the publication: T. Ringbeck & B. Hagebeuker “A 3D Time of Flight Camera for Object Detection”, 8th Conference on Optical 3-D Measurement Techniques, ETH Zurich, 2007. The publication shows a PMD-3D camera which transmits its modulation signal via an LVDS line to an IR searchlight.
In addition, the following publication also deals with the use of a PMD camera in a vehicle: H. Schoepp, A. Stiegler, T. May et al. “3D-PMD Camera Systems to Acquire Vehicle Surroundings and to Monitor the Vehicle Interior”, 13th International Congress on Electronics in Vehicles, VDI Vehicle and Traffic Technology, Baden-Baden, V D I, 2007. The publication shows an IR light source of the PMD system integrated into a radiator grill. The light source is controlled via an LVDS connection, while the modulation signal and also the diagnostic data of the illumination units are fed back to the camera via a LIN bus.
An LVDS system is known from U.S. Pat. No. 7,482,837 B2, in which in addition to the actual data signal a clock signal is also transmitted via the LVDS line. On the transmission side, an LVDS generator and an offset modulator, which acts on the LVDS line, are provided. The potentials are consolidated and transmitted to the receiver via the LVDS line. On the receiver side, the offset voltage is demodulated and a clock signal is determined. As usual, the transmitted data is obtained from the LVDS signal.
A TOF camera system with signal path monitoring is known from WO 2102/013760, in which the illumination and the TOF camera are arranged in separate modules. The signals are preferentially exchanged electrically between both modules, wherein the transmission can occur, for example, via an LVDS signal.